1. Field of the Invention
The present invention relates to a technology of producing a fine structure such as a semiconductor, MEMS, a photonic crystal, a micro flow path, μTAS, and Lab-on-Chip; and to a technology of forming a hollow laminate structure.
2. Description of the Related Art
A hollow fine structure can be used to make a filter or the like by a method such as gas suspension in a resin; in order to fabricate its inner structure with good reproducibility, there has been used a method such as printing and photolithography wherein a replication is done by using an original plate.
In general, a burying material is used to bury concavity and convexity on a substrate; in order to produce a hollow structure, its surface needs to be ground down till the outermost surface of the structure on the substrate is exposed. This is often called a sacrificial material when its function is included.
In production of a semiconductor or MEMS, a laminate having a hollow structure can be produced by a method in that, by making use of the difference in etching rate between a structural material and a sacrificial material to be buried between the structural material, after formation of a sacrificial material, for example a silicon oxide layer, and patterning thereafter, a structural material, for example polysilicon, is deposited, it is then subjected to patterning again, and then the sacrificial material is removed by etching to obtain a hollow structure. In this case, to obtain a multilayer, flattening of the surface as well as flattening to connect the structural materials themselves are necessary. By repeating these steps, a photonic crystal, for example, a three-dimensional wood pile structure, can be obtained. However, the processes are widely diverse, requiring an exposure equipment, equipments for CVD and etching, CMP, and the like; and thus its fabrication is not easy.
In a micro flow path, μTAS, and Lab-on-Chip, a molding method called a LIGA process or a LIGA-like process (a method in that a mold is formed and a structure is fabricated by pressing the mold to a structural material or casting a structural material into the mold), and a method called a resist molding method (a method in that a film is formed on a resist pattern by a structural material such as a resin and a metal alkoxide by using the resist pattern as a template, and then the resist pattern is removed through an opening thereby fabricating a hollow structure such as a flow path) are reported.
In any of the fabrication methods, a sacrificial layer that forms an opening on top of the hollow structure and supports a beam and a ceiling made of a structural material is necessary; thus formation of the sacrificial layer and final removal of the sacrificial layer tend to be complicated in the fabrication process.
Especially, in the burying step, a part other than the buried part in the sacrificial layer needs to be removed thereby exposing surface of the structural material. Thus, the resist molding method, which involves patterning of a buried part of a resist composition first thereby making the resist composition a sacrificial layer, is more convenient; but it is not a means for solving the problem in the method of forming an opening of the structural material to finally remove the resist composition of the sacrificial layer.
In Japanese Patent Laid-Open Publication No. 2008-299165, a method for fabricating a hollow structure by making use of the difference in photo-sensitivities to the wavelength of the light between two photo-sensitive layers is proposed; in this method, in fabricating the structure on and after the second layer, deterioration of the structural resistance due to the hollow structure remained intact in the process becomes a problem as the number of the layers increases. Even if, in order to form the hollow at the final step, development is done after exposure of the multilayer is finished, there are problems of resolution deterioration of the pattern of a underlying photosensitive layer accompanied with the lapse of time and repeat of the heating process, and of repeating precision to obtain an intended form. A layer sensitized by the light with the wavelength longer than 400 nm has also a restriction in resolution.